ALGIERS - Militants may be planning to attack commercial aircraft in Algeria, the US and British governments told nationals living in the oil- and gas-exporting North African country.

A US embassy warden's message dated March 12 said: "There is information that extremists may be planning to conduct an attack against a commercial aircraft carrying Western workers in Algeria."

A similar Britain travel advice statement dated March 13 said: "We are aware of reports that terrorists may be planning to carry out attacks against aircraft flying into Algeria. We are liaising with the local authorities."

Islamist rebels have attacked foreigners working in Algeria's lifeline energy sector twice in recent months and have also stepped up a campaign of bombings against Algerian police.

In the first attack on foreigners, on December 10, insurgents set off a roadside bomb on the outskirts of Algiers beside a bus carrying Western oil workers, including Americans and Britons, killing an Algerian and a Lebanese and wounding four others.

The second attack, on March 3, 130km southwest of Algiers, on a bus carrying workers for a Russian gas pipeline construction firm, killed three Algerians and a Russian.

The attacks were claimed by the al Qaeda Organisation of the Islamic Maghreb, a group of Algerian Islamist rebels formerly known as the Salafist Group for Preaching and Combat (GSPC) who adopted the new name in January to deepen ties to al Qaeda.

The attacks on foreigners, plus a spate of other bombings in urban areas, are a sharp change from the GSPC's habitual small-scale kidnappings, ambushes, fake roadblocks and assassinations in remote rural areas.

"The threat from terrorism in many areas continues to pose a significant security risk," the US State Department's standing travel advice for Algeria says.

"Security in Algiers has been stepped up sharply in recent weeks, with increased roadblocks and vehicle searches across the city and plainclothes police stopping and questioning pedestrians in some areas."

Some security analysts say the GSPC wants to transform itself from a domestic rebellion in Algeria, where it is under pressure from security forces, into an international force capable of striking in both North Africa and in Europe.

Founded in 1998, the GSPC began as an offshoot of another armed group that was waging an armed revolt against the government to establish an Islamic state.

The GSPC has shared the overall aims of that revolt, which began in 1992 after the then military-backed authorities, fearing an Iran-style revolution, scrapped a parliamentary election that an Islamist political party was set to win.